Will a dimmer switch that is used to slow the speed of my 1/3 horse GE motor damage the motor?

I am going to use it to turn a spit for hog roasting. I already have a gear reduction box which is 30 to 1, so instead of using another set of pulleys or sprockets, I thought that this might work instead.

Field of Industry:: Retired with an upper case R!! (forgot how to spell capital)